Many applications require the monitoring or control of fluid flow through a conduit or interface. For example, valves are used to control liquid or gas fluid flow through a pipe or conduit. To control the flow of the liquid, a valve is opened or closed. In many systems, liquid flow is automatically-controlled using an actuator connected to a valve. Responsive to control signals, the actuator causes the valve to be further opened or closed as necessary to achieve a desired liquid flow.
In another example, ventilation dampers are used to control the flow of air into ventilation ducts, rooms, or other spaces of a building or facility. For example, a ventilation damper may control the flow of cool air in to a room. In other examples, a ventilation damper may control the amount of exhaust air from a room, and/or the amount of recirculated and fresh air that is provided throughout a building. Ventilation dampers are movable such that they may be further opened or closed in order to increase or decrease, respectively, the flow of air through the damper assembly device. In building control systems, damper assembly devices are also known as variable-air-volume (VAV) diffusers or VAV units.
One example of a VAV unit and its operation is set forth in U.S. Pat. No. 6,581,847, which is incorporated herein by reference. The VAV unit of U.S. Pat. No. 6,581,847 teaches the control of room temperature using a VAV unit to vary the volume of supply air discharged into a room. The supply air is heated when the VAV unit is in a heating mode and is cooled when the system is in cooling mode. The supply air is usually provided at substantially a constant temperature in each mode. A VAV unit regulates the volume of heated or cooled supply air in order to achieve and maintain a desired room air temperature. To this end, a controlled actuator device operates to open or close a set of louvers or ventilation dampers to increase or decrease the flow of supplied air.
Typical controlled actuator devices include thermally-powered actuators, pneumatically-powered actuators, and electrically powered actuators. All three types of actuators are coupled to the ventilation dampers by a mechanical linkage, gear assembly levers and/or combinations of these and other mechanical couplings. The actuator performs controlled movements which are translated by the mechanical couplings to changes in the positions of the dampers.
Control units for liquid control valves and VAV units often maintain accurate information regarding the current position of the valve or damper. Accurate position information is useful for various reasons, including effective control and reliability. Inaccurate position information can even result in damage to a valve or VAV unit. In one example, if a damper is fully open, and the position information indicates that the damper is not fully open, then the control mechanism may attempt to further open the damper. The attempt to further open the damper that is already fully open is both inefficient and potentially harmful to the equipment.
In addition, VAV units and liquid control valves often have associated flow sensors to determine the actual flow of fluid (gas or liquid) through the damper or valve. Ultimately, it is the flow of the fluid that is to be controlled, and thus information regarding the flow of fluid through the valve or damper provides feedback which may be used to determine whether the valve or damper should be further opened, or further closed. However, air flow sensors and water flow sensors typically require several parts including differential pressure sensor elements, tubing and pickups. These elements contributed to the cost of both parts and labor, as several parts must be added and then wired.
Accordingly, there is a need for fluid flow control arrangements with improvements in fluid flow sensing technology that address at least some of the issues discussed above.